At present, it is required to highly integrate semiconductor elements in order to promote performance advancement in semiconductor devices such as random access memories and flash memories. For attaining the high degree of integration of semiconductor elements, it is essential that a technique for forming a thin film having an even thickness on the surface of a fine three-dimensional structure should be established and put to practical use. The CVD method, in which a gaseous material is decomposed on a substrate to deposit a film, or the atomic layer deposition method (ALD method), in which a material adsorbed on a substrate surface is decomposed to deposit a film, is attracting attention as a promising candidate for that technique. Investigations are presently being made in order to put these techniques into practical use.
Substances having a high vapor pressure and thermal stability are selected as materials to be used for forming a thin film by the CVD method or ALD method. For forming thin films of constant quality, it is important to precisely control the concentration of the material during thin-film formation. From this standpoint, liquid materials are preferred materials for thin-film formation because the rate of vaporization thereof is easier to control than that of solid materials.
Titanium oxide and titanium-containing oxides are regarded as candidates for materials for the capacitor dielectric films of next-generation and succeeding dynamic random access memories (DRAMs). Titanium-containing oxides are regarded also as a candidate for, for example, a material for the ferroelectric film of a non-volatile memory.
Titanium tetrachloride TiCl4, tetraisopropoxotitanium Ti(OiPr)4, and the like have been investigated hitherto as materials for forming a titanium-containing thin film by the CVD method or the ALD method.
Some attempts have been made to incorporate a chelate ligand in order to control the reactivity of Ti(OiPr)4 with water. For example, titanium compounds having one or more chelate ligands, such as (diisopropoxo)(bis(2,2,6,6-tetramethylheptanedionato))titanium (Ti(OiPr)2(THD)2), diisopropoxobis(tert-butylacetoacetato)titanium (Ti(OiPr)2(tbaoac)2), bis(dimethylaminoethoxo)-diisopropoxotitanium (Ti(OiPr)2(dmae)2), and (dimethylaminoethoxo)triisopropoxo-titanium (Ti(OiPr)3(dmae)), have been synthesized and are being investigated as materials for use in the CVD method or the ALD method. (Non-patent documents 1, 2, 3, and 4).
Furthermore, titanium compounds having amide ligands are also being investigated as materials for forming a thin film by the CVD method or the ALD method. For example, formation of a thin titanium nitride film, thin titanium oxide film, or the like by the CVD method or ALD method using tetrakis(dimethylamido)titanium (Ti(NMe2)4) as a material is being investigated. (For example, non-patent documents 5 and 6). Amidotitanium complexes having a chelate ligand are also being investigated as materials for thin-film formation. Examples thereof include the titanium complexes described in patent document 1.
Moreover, an aryloxo complex which is similar in structure to the titanium complex of the present invention because of the possession of an ethene-1,2-diyldiamide ligand is known. (Non-patent document 7)